xchg() and cmpxchg()

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From: H. Peter Anvin
Date: Tuesday, July 27, 2010 - 4:57 pm

Okay, I've stared at this issue for most of the day, and I have a fix
for the immediate issue.

However, I also am convinced that the whole scheme with the __xg() macro
is just broken.  It was introduced in 1.3.11 when xchg and cmpxchg where
neither "asm volatile" nor had "memory" clobbers as an apparent way to
keep gcc from moving memory references around it, but since the array
type is "unsigned long" rather than a char type, it probably doesn't
even work right, and with asm volatile/memory clobber it should not be
necessary.

At this point I'd like to push an urgent patch to fix the immediate
issue, and a cleanup patch getting rid of __xg() for .36.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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Messages in current thread:
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Tue Jul 13, 11:21 am)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Tue Jul 13, 4:49 pm)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 10:19 am)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 10:34 am)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 10:57 am)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 11:15 am)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 1:40 pm)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 1:58 pm)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 2:11 pm)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 2:11 pm)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Wed Jul 14, 2:11 pm)
Re: [patch 134/149] x86, paravirt: Add a global synchroniz ..., Jeremy Fitzhardinge, (Tue Jul 27, 10:46 am)
xchg() and cmpxchg(), H. Peter Anvin, (Tue Jul 27, 4:57 pm)
[tip:x86/urgent] x86: Add memory modify constraints to xch ..., tip-bot for H. Peter ..., (Tue Jul 27, 10:33 pm)
[tip:x86/asm] x86, asm: Clean up and simplify <asm/cmpxchg.h>, tip-bot for H. Peter ..., (Wed Jul 28, 4:28 pm)
[tip:x86/asm] x86, asm: Move cmpxchg emulation code to arc ..., tip-bot for H. Peter ..., (Thu Jul 29, 1:12 pm)
[tip:x86/asm] x86, asm: Merge cmpxchg_486_u64() and cmpxch ..., tip-bot for H. Peter ..., (Thu Jul 29, 1:13 pm)
Re: [tip:x86/urgent] x86: Add memory modify constraints to ..., Jeremy Fitzhardinge, (Mon Aug 2, 4:51 pm)
Re: [stable] [tip:x86/urgent] x86: Add memory modify const ..., Tomáš Janoušek, (Thu Sep 9, 12:53 pm)
Re: [stable] [tip:x86/urgent] x86: Add memory modify const ..., Tomáš Janoušek, (Thu Sep 9, 2:09 pm)
Re: [stable] [tip:x86/urgent] x86: Add memory modify const ..., Tomáš Janoušek, (Fri Sep 10, 6:10 am)
Re: [stable] [tip:x86/urgent] x86: Add memory modify const ..., Tomáš Janoušek, (Fri Sep 24, 12:17 am)